It is known that rubber scrap may be reduced to a useful fine size for recycling by grinding between abrasive grinding stones until the rubber is reduced to particle sizes of a fineness of 40 mesh or finer. Such abrasively ground rubber has beneficial properties in many uses and provides a constituent which may be recycled into both rubberized plastic products for beneficial physical properties or mixed with other materials to form useful compounds.
The prior art exemplified by British Patent 1,516,090 to Robinson et al., a series of patents currently owned by the Goodyear Tire and Rubber Company of Akron, Ohio, exemplified by Brubaker et al. U.S. Pat. No. 4,469,284, and applicant's prior issued U.S. Pat. No. 5,238,194 disclosing an improved method of grinding a rubber slurry to produce fine particulate rubber particles.
Prior art rubber comminuting utilizes a form of vertical grinding apparatus adapted from an abrasive grinder long used in the paint and pigment industry for the grinding of organic and metallic pigments for incorporation in paints. This apparatus utilizes a pair of opposed grinding stones: a top stone which is fixed to a plate adjustable vertically in spacing from and opposed face to face to a horizontally mounted grinding stone which is set upon a motor to rotate around a vertical axis. Both stones have hollow centers and grind ion mating faces which have the form of a flat torus. In each case the material to be ground is introduced as a slurry through an opening in the top stone to an open center space formed by the open centers of the stones. The rubber containing slurry passes between the two opposing faces during the grinding process and the ground slurry is collected in a collection region outside the outer rim of the stones and then further processed by screening, drying and the like to separate out the finely ground output rubber.
These mills, being designed for fine pigment production for paint, have a limited output production rate for producing similarly fine ground rubber. While various techniques, such as is shown in our prior patent for an improved method for grinding rubber, have increased the through put of finely ground rubber in a given period of time, these artificial pigment grinding machines have a definite upper practical production limit.